Eryngium planum (E. armatum, E. caeruleum, E. intermedium, E. latifolium, E. planifolium) | Flat Sea Holly ‘Jade Frost’
Sea Holly has been grown in American gardens since the 1800’s. Its an easy-to-grow fancy thistle with beautiful metallic, almost iridescent, bright blue, thistle-like flowers that sit atop 3 ft tall plants. The ‘Jade Frost’ varieties blooms are cream when they first appear, then turn blue, creating bicolor blooms on one plant. As they age, the spiny narrow bracts turn blue. The blue color of the flower will intensify in higher temperatures. What makes ‘Jade Frost’ Sea Holly so special though is the low-growing blue-green foliage that has a stunning creamy white margin along the edges. When night temps are still cool, the young leaves may even have a pink-tinge to them. Deer- and rabbit-resistant, sea holly’s foliage looks great even before the flowers take off.
Sea Holly plants love sunshine and normal or sandy soil, and once established, they are extremely drought resistant and require little care. They make great specimens for low-water gardens. Seeds can be started directly outside by scattering outside in late autumn or can be started indoors, but may require vernalization/ stratification. Move seedlings to their permanent location when they are still small because Eryngium have large taproots and won’t transplant well once mature.
The species is hermaphrodite (has both male and female organs) and is self fertile. Eryngium plants may or may not flower the first year from seed, but should come back with a vengeance in following years. They are valued by many for their prolonged bloom time. If you deadhead them they will keep blooming well into fall. Seeds will self-sow, but not to the point of becoming invasive.
These plants attract bees, flies, butterflies, beetles, and other pollinators like crazy! This was our garden-winner for ‘most visited’ by pollinators as well as having the most diverse group of pollinators too! Plus are deer and rabbit resistant.
Almost all Eryngium make excellent, long lasting cut flowers. Harvest them when the entire flower heads and bracts turn blue so the flowers will keep their beautiful blue color after drying.
Sun exposure: Full sun
Mature height: 3 ft
Mature width: 2 ft
Hardiness zones: 4- 9